Patent Application
20130115855
This application is based upon and claims benefit of priority from the Japanese Patent Application No. 2011-244581, filed on Nov. 8, 2011, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a polishing method and a polishing apparatus.
When a thin film and a substrate surface are planarized in a manufacturing process of an LSI device and so on, a chemical mechanical planarization method (CMP method) has been put to practical use. With miniaturization of an LSI device and reduction in the cost, there is required a CMP technique of processing a device surface into flatter, a lower level of defects, and more inexpensively.
In the CMP method, since slurry (polishing agent) containing polishing abrasive grains is used, there is a problem that scratches (polishing flaw) caused by abrasive grain residues cannot be prevented completely. Although the number of scratches and the size can be suppressed with improvement of the CMP method, with the miniaturization of the LSI device, in the future a construction of a several nm order is required to be processed without damage. For example, in a STI (Shallow Trench Isolation) process in LSI manufacture, a SiO2 film formed on the entire surface while covering a minute groove pattern is polished and removed without damage by the CMP method, and the SiO2 film is required to be embedded only in the groove. Since a transistor is formed on the polished surface, it is especially required to suppress scratches.
For the above problem, there has been known CMP temperature control as the CMP technique with high flatness, a low level of defects, and high productivity. In conventional CMP temperature control, air is jetted toward a polishing pad surface in CMP, and the pad surface and slurry on the surface are cooled. However, this method is cooling utilizing heat of vaporization of the slurry according to air blow, and the cooling capacity is insufficient.
Meanwhile, in order to suppress scratches, CMP is required to be performed after removing residues and foreign matters on the polishing pad. As a conventional removal method, a diamond dresser is pressed against the polishing pad surface between polishing operations, and the pad surface is scraped by approximately 1 μm and cleaned while flowing a cleaning liquid such as purified water. This cleaning is called dressing. The diamond dresser is a disk with a large number of minute industrial diamonds arranged on the surface. When diamond microparticles are dropped, this is a major cause of a large scratch. Although it is preferable to perform dressing in the CMP process in terms of productivity of LSI, the diamond microparticles may be dropped; therefore, dressing is performed between the polishing operations, and this interferes with the improvement of the productivity.
The polishing pad is generally formed of foamed polyurethane, and the pore diameter of a foam is several ten μm. Since a foam portion is exposed on the polishing pad surface, a myriad of pores with a depth of several ten μm appear on the pad surface. In order to enhance slurry retention capacity, a large number of vertical holes with a depth of several hundred μm are often formed in the pad surface. Thus, a large number of the pores with a depth of from several ten μm to several hundred μm are formed in the pad surface. Although the polishing pad surface can be cleaned by the diamond dresser, polish residues and foreign matters accumulated in a deep portion of each pore cannot be removed, and thus the polish residues discharged from the pores may cause scratches.
According to one embodiment, a polishing method comprises pressing a substrate being rotated against a polishing pad being rotated and supplying slurry on the polishing pad, measuring a surface temperature of the polishing pad, and when the surface temperature is not less than a predetermined temperature, jetting jet stream containing supercooled droplets from a nozzle having a narrow portion toward the polishing pad.
Before the description of an embodiment of the present invention, a background that the present inventors made the present invention will be described.
In the following embodiment, the above problem can be solved. Hereinafter, the embodiment of the present invention will be described based on the drawings.
The top ring 11 is provided with an air cylinder mechanism (not shown) adding a load to the top ring 11. In the top ring 11, a wafer (substrate) W as a polished body is held by a vacuum chuck through an elastic member (not shown) such as rubber. The top ring 11 is connected to a drive mechanism (not shown) and can be moved and rotated in a vertical direction by the drive mechanism.
The polishing table 12 is arranged below the top ring 11, and a polishing pad 13 is applied onto the upper surface of the polishing table 12. The polishing table 12 can be rotated by a drive mechanism (not shown).
The supply nozzle (supply unit) 14 is provided above the polishing table 12 and supplies the slurry onto the polishing pad 13.
The Laval nozzle 15 jets jet stream containing supercooled droplets onto the polishing pad 13 to cool the surface of the polishing pad 13. As shown in
For example, as shown in
The compressed air and the flow rate of water supplied to the Laval nozzle 15 can be controlled by a jet stream control unit 21 shown in
The water supplied to the Laval nozzle 15 becomes a large number of minute droplets by a high-pressure air jet stream. Since the nozzle diameter of the Laval nozzle 15 is expanded downstream from the throat portion, minute water droplets are cooled to a supercooling temperature by adiabatic expansion. When the supercooled droplets reach on the polishing pad 13, they are frozen, and the surface of the polishing pad 13 and the slurry can be efficiently cooled by the fusion heat and vaporization heat according to high-pressure air.
As shown in
Next, a method of polishing a polished body using the polishing apparatus 1 will be described using a flow chart shown in
(Step S101)
The wafer W as the polished body is held by the top ring 11.
(Step S102)
The top ring 11 and the polishing table 12 are rotated by a drive mechanism. The top ring 11 is lowered downward, and the wafer W is pressed against the polishing pad 13 with a certain load. The slurry is supplied onto the polishing pad 13 from the supply nozzle 14 in this state, whereby polishing is performed.
(Step S103)
The surface temperature of the polishing pad 13 is measured using the temperature sensor 16. The surface temperature is gradually increased by frictional heat and an intentionally added heat source. When the surface temperature is not less than a predetermined temperature, the process proceeds to step S104.
The predetermined temperature is, for example, a temperature at which the slurry is deteriorated (a temperature at which a complex-forming agent, an oxidizing agent, and so on contained in the slurry are thermally decomposed) and is changed according to components of the slurry.
(Step S104)
The jet stream control unit 21 jets the supercooled droplets from the Laval nozzle 15 to the polishing pad 13.
(Step S105)
When the surface temperature of the polishing pad 13 is lowered to less than a predetermined temperature, the process proceeds to step S106. When the surface temperature is not lowered, the process proceeds to step S107.
(Step S106)
The jet stream control unit 21 adjusts the flow rate of high-pressure air supplied to the Laval nozzle 15 so as to prevent the surface temperature of the polishing pad 13 from being not less than a predetermined temperature. At this time, the jet stream control unit 21 adjusts the flow rate of the high-pressure air supplied to the Laval nozzle 15 so as to prevent the surface temperature from being lowered too much. This is because when the temperature is too low, the polishing performance of the slurry is lowered. Accordingly, the jet stream control unit 21 adjusts the flow rate of the high-pressure air supplied to the Laval nozzle 15 so that the surface temperature of the polishing pad 13 falls within a predetermined range.
(Step S107)
The jet stream control unit 21 increases the flow rate of the high-pressure air supplied to the Laval nozzle 15 so that the surface temperature of the polishing pad 13 is less than a predetermined temperature. The flow rate of the high-pressure air is increased, whereby the temperature of the supercooled droplets jetted from the Laval nozzle 15 is lowered.
As described above, according to the present embodiment, when the surface temperature of the polishing pad 13 is not less than a predetermined temperature, the supercooled droplets are jetted to the polishing pad 13, whereby the surface of the polishing pad 13 and the slurry can be quickly cooled by the fusion heat and vaporization heat according to the high-pressure air. In the cooling using the supercooled droplets, the cooling rate is about six times (time required for cooling is about ⅙) in comparison with a conventional air blow method (cooling only according to slurry vaporization heat).
Accordingly, the polishing pad and the slurry can be efficiently cooled by the polishing method and the polishing apparatus according to the present embodiment.
In the above embodiment, when the surface temperature of the polishing pad 13 is not less than a predetermined temperature, the supercooled droplets are jetted. However, a relationship between the rotation speed of the top ring 11 and the polishing table 12 and a variation with time of the surface temperature of the polishing pad 13 is previously investigated, and the supercooled droplets may be jetted according to whether or not the time when the surface temperature increases to a predetermined temperature has elapsed.
As shown in
The polishing apparatus 1 shown in
In the dressing using the polishing apparatus 1, since the diamond dresser is not used, there is no possibility that a large scratch associated with drop of the diamond microparticles is created. Accordingly, dressing is not required to be performed between the polishing of one polished body and the polishing of the next polished body, and since dressing can be performed during the polishing operation, the productivity can be enhanced.
The polishing apparatus according to the present embodiment is used thus, so that dressing of the polishing pad surface can be efficiently performed.
Water (purified water) supplied to the Laval nozzle 15 is replaced with organic acid dissolving residues or a surfactant water solution, whereby the performance of dressing can be further enhanced. The organic acid may become a soluble reactant by, for example, forming a complex with residues. The soluble reactant is used because it can be removed in subsequent water rinsing process.
In the dressing using water jetting, the amount of purified water to be used is extremely large such as not less than several liters per minute, and, at the same time, if the large amount of water is flowed during the CMP process, the slurry is substantially diluted to lower the polishing performance. Thus, the dressing using water jetting has to be performed between the polishing operations, and the dressing cannot be efficiently performed unlike the case of using the polishing apparatus 1.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-244581 | Nov 2011 | JP | national |
